We have examined the ultrastructural changes that take place during spermiogenesis in the rhea. Spermatozoa are characterized by a curved head and a midpiece. A thin rod extends from the anterior tip of the spermatozoon through the center of the nucleus. A 3-mu-long distal centriole occupies the entire midpiece. The principal piece is characterized by a small fibrous sheath and tiny dense fibers that are only observed in the region of the principal piece, which is immediately behind the annulus. During development a circular manchette surrounds the nucleus of young spermatids. Later the microtubules of the circular manchette become reorganized into a longitudinal manchette. A long distal and short proximal centriole are observed in early round spermatids. The distal centriole becomes associated with the plasma membrane. Later the proximal centriole is observed in association with the nucleus. The area around the centriole pair then accumulates dense material, which is associated with either the centrioles or the circular manchette. The longitudinal manchette forms and then disappears and mitochondria subsequently associate with the distal centriole. The long centriole of the rhea enables this species to develop a midpiece similar to the midpiece of mammalian sperm without the complex intercellular movements that characterize mammalian spermiogenesis.

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Zoos and other ex situ wildlife institutions can play an important role in species conservation by maintaining populations for education and research, as sources for potential re-introduction or reinforcement, and as ambassadors for financial support of in situ conservation. However, many regional zoo associations are realizing that current captive populations are unsustainable, with many programs failing to meet demographic and genetic goals to ensure long-term viability. Constraints on population size due to limited space often mandate delayed and/or less frequent breeding, but for females of many species this can have profound effects on fertility. A retrospective analysis combined with published literature and reliable anecdotal reports reveals that, when females are housed in a non-breeding situation for extended periods of time, reproductive changes that negatively impact fertility have occurred in multiple species, including canids, elephants, white rhinoceros, Seba's bats, wildebeest, stingrays, and some felid species. Competing space needs and changing interest in taxa for exhibits over time compound the problem. Counter strategies to breed early and often have their own demographic and genetic consequences as well as logistical and political implications. Strategies to mitigate the sustainability crisis in these taxa might include a mixed strategy in which young, genetically valuable females are bred earlier and at more regular intervals to ensure reproductive success, in combination with the judicious use of available tools to manage the number of offspring produced, including contraception and culling. An understanding of the issues at stake is the first step towards developing management strategies for sustainable populations.

Using artificial insemination we attempted to produce hybrids between captive, male, western, gray wolves (Canis lupus) and female, western coyotes (Canis latrans) to determine whether their gametes would be compatible and the coyotes could produce and nurture offspring. The results contribute new information to an ongoing controversy over whether the eastern wolf (Canis lycaon) is a valid unique species that could be subject to the U. S. Endangered Species Act. Attempts with transcervically deposited wolf semen into nine coyotes over two breeding seasons yielded three coyote pregnancies. One coyote ate her pups, another produced a resorbed fetus and a dead fetus by C-section, and the third produced seven hybrids, six of which survived. These results show that, although it might be unlikely for male western wolves to successfully produce offspring with female western coyotes under natural conditions, western-gray-wolf sperm are compatible with western-coyote ova and that at least one coyote could produce and nurture hybrid offspring. This finding in turn demonstrates that gamete incompatibility would not have prevented western, gray wolves from inseminating western coyotes and thus producing hybrids with coyote mtDNA, a claim that counters the view that the eastern wolf is a separate species. However, some of the difficulties experienced by the other inseminated coyotes tend to temper that finding and suggest that more experimentation is needed, including determining the behavioral and physical compatibility of western gray wolves copulating with western coyotes. Thus although our study adds new information to the controversy, it does not settle it. Further study is needed to determine whether the putative Canis lycaon is indeed a unique species.

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